Regev – You can reset the time remaining calculations on your Paperwhite as follows:
1) Open up any book
2) Search for ;ReadingTimeReset
– include the leading semicolon, and note that it is case sensitive and there are no spaces
3) You will get 0 search results
4) Hit the back button/icon.
Your books will now show “learning reading speed”. After a bit of reading your speed, and thus time remaining, will be recalculated.

Using the key provided to you (MSDN etc.) you will need to run the following in an elevated command prompt –
if you are new to Windows 8, click Start –> type “cmd” –> right-click on a command prompt and select “Run as administrator” in the bottom of the page:

Next type the following commands:

slmgr.vbs /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

slmgr.vbs /ato

The first command will update the key.

The second command will activate Windows.

Replace the “XXXX” bits with your Windows 8 Key (you do need to enter the dashes and you don’t need to surround it with double quotes).

I made sure USB debugging was on. And that MTP was on. Still nothing. So set MTP to Charging, wait for Windows to do the drive thing again. Then set back to MTP. Drivers do their thing again and there are the folders. Finally.